Fuel injection system for internal combustion engines

ABSTRACT

An improvement in a fuel injection system for internal combustion engines and particularly for diesel engines is described wherein a pump-and-nozzle assembly comprising a top part, a pump part and an injection nozzle part is provided for each of the cylinders in the engine comprises a 3:2-path solenoid valve being disposed near a slide valve controlling the pump part of the assembly and establishing communication between a pressure source and the said valve slide, a pre-set nozzle member influencing the velocity of the intake stroke of a pump piston in the pump part of the assembly, and a 2:2-path solenoid valve interposed in a fuel return line and comprising adjusting means for comprising the opening periods thereof and thereby determining the duration and length of the intake stroke of the pump piston and together therewith the amount of fuel deliverable from the pump part to the nozzle part of the assembly in the interval between two fuel injections.

[ Sept. 24, 1974 FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES [75] Inventor: Heinz Links, Stuttgart, Germany [73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: Mar. 13, 1973 [21] Appl. No.: 340,713

[30] Foreign Application Priority Data Mar. 22, 1972 Germany 2213776 [52] US. Cl. 123/139 E, 123/32 AE, 123/140 MC [51] Int. Cl F02m 51/00 [58] Field of Search 123/139, 140, 32

[56] References Cited UNITED STATES PATENTS 1,664,610 4/1928 French 123/32 AE 3,464,627 10/1969 Huber 123/139 E 3,665,907 5/1972 Laufer 123/139 E 3,680,537 8/1972 Suda 123/139 E Primary Examiner-Laurence M. Goodridge Assistant Examiner-Cort Flint Attorney, Agent, or Firm--Edwin E. Greigg [5 7] ABSTRACT An improvement in a fuel injection system for internal combustion engines and particularly for diesel engines is described wherein a pump-and-nozzle assembly comprising a top part, a pump part and an injection nozzle part is provided for each of the cylinders in the engine comprises a 3:2-path solenoid valve being disposed near a slide valve controlling the pump part of the assembly and establishing communication between a pressure source and the said valve slide, a pre-set nozzle member influencing the velocity of the intake stroke of a pump piston in the pump part of the assembly, and a 2:2-path solenoid valve interposed in a fuel return line and comprising adjusting means for comprising the opening periods thereof and thereby determining the duration and length of the intake stroke of the pump piston and together therewith the amount of fuel deliverable from the pump part to the nozzle part of the assembly in the interval between two fuel injections.

8 Claims, 6 Drawing Figures AIEmmsEmwn 3.837.824

Sum anr a PAIENIED SEP 2 41874 I SHEH 5 0F 6 Fig.5

Qmax. Hmax.

Qt Ht PAIENTEDsarzmen WSW Fig. 5

FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION This invention relates to a fuel injection system for internal combustion engines, and in particular for diesel engines, and is of the type comprising a pump-andnozzle assembly per working cylinder. The pump piston in this assembly is driven by means of a servo piston of larger diameter, and the assembly is connected to a pressure source which supplies fuel to the work space of the pump as well as, via a fuel supply valve, to a servo pressure space which is limited on one side thereof by a frontal end of the servo piston. The system further comprises a slide valve the slide of which is controlled by a control device synchronously with the engine and which is operated by a portion of the fuel tapped from the pressure source and serving as an auxiliary control liquid; in its first indexing position, the valve slide controls the flow of fuel to the servo pressure space, and in its second indexing position, it controls the flow of fuel from the servo pressure space to a fuel return line, while at the same time triggering the return stroke of the servo piston and simultaneously therewith the intake stroke of the pump piston.

In a known fuel injection system of this type, the control device is a mechanically driven rotary distributor serving all pump -and-nozzle units of the engine in common, and controlling the flow of auxiliary control liquid to the slide valve during switching times which are determined exactly by the construction of the distributor. Due to the long flow paths which are characteristic for this type of system and which are, moreover, of greatly differing lengths especially in larger engines, and due to the mechanical control of the switching times, it is difficult to achieve a control operation which is sufficiently rapid and exact to satisfy the demands of modern engines. A known fuel injection system of this type operates in dependence on the rpm of the engine,'as the switching times of the engine-driven rotary distributor vary with the rpm; to these variations there must be added the variations in the throttle effect at the control passages, all of which makes it difficult to adjust the amount of fuel to be injected to a constant rate at rapidly changing rpms.

In another known fuel injection system of similar construction, the slide valve is mechanically connected to the armature of an electromagnet and is driven by the armature synchronously with the internal combustion engine. This system suffers from the drawback that the forces due to inertia of the armature and of the valve slide render a sufficiently rapid and exact operation difficult or impossible, especially in high speed diescl engines. As the armature of the electromagnet must effect long strokes in order to shift the valve slide from one to the other of its two indexing positions, and must be correspondingly large in view of the masses to be moved, a further drawback of this system resides in the very sluggish response of the magnet and its excessively long switching time.

OBJECT AND SUMMARY OF THE INVENTION It is a primary object of the invention to avoid the abovementioned drawbacks and to provide a fuel injection system which operates sufficiently rapid and exact, especially in high-speed diesel engines, and in which the injected fuel amount can be maintained constant independently of rapidly varying rpms.

This and other objects which will become apparent hereinafter, are attained by a fuel injection system according to the invention wherein each pump-andnozzle unit has a control device comprising a solenoid valve devised as a 3:2-path valve which is arranged close to a valve slide, and which connects a pressure source with the slide valve when in on position, whereby the slide is moved to its first indexing position triggering the beginning of the fuel injection; wherein each pump-and-nozzle unit further comprises between the pressure source and a fuel feeder valve a fixedly set throttle member influencing the velocity of the intake stroke, and wherein a second solenoid valve devised as a 2:2-path valve is disposed in a fuel return line and determines, when the slide is in its second indexing position, and due to its variable opening time, the duration and length of the intake stroke and thereby also the amount of injection fuel to be accumulated between two successive injections.

By means of the separate control of the beginning of injection and of the amount of fuel to be injected, each by a different solenoid valve, the moment of beginning the injection and the amount to be injected can be adjusted very accurately and within narrow limits to the actual operational conditions of the engine. By having the throttle means disposed upstream of the feeder valve a fuel intake time can be attained which is substantially longer than the injection time, whereby a correspondingly greater accuracy in metering the amount of fuel to be injected can be achieved; due to the prolonged fuel intake time, it is possible to control even very small amounts of injection fuel very exactly. The fuel injection system according to the invention also permits preliminary injections and interrupted injections to be obtained by a corresponding control of the two solenoid valves, which control can be effected in the case of the known injection systems only by means of cumbersome auxiliary devices.

A particularly advantageous embodiment of the fuel injection system according to the invention comprises an arrangement wherein the second solenoid valve is disposed in the fuel return line and determines the duration of the intake strokes of at least two pump-andnozzle units. Thereby, the required number of solenoid valves of the second above described kind in the engine can be reduced at least by half.

A further advantageous embodiment of the invention provides means for determining the largest admissible amount of injection fuel by means of the maximum possible stroke of the pump piston. This makes it impossi' ble to inject more than the admissible amount of fuel in one injection operation. This is of importance especially in the operation of diesel engines and is particularly advantageous when the aforesaid admissible fuel amount is equal to the fuel amount required to be injected for operation under full load. This prevents the feared expelling of unburned exhaust gases which occurs when there is an excess of fuel, and in violation of legislation for preserving a pure atmosphere.

A further advantageous embodiment of the fuel injection system according to the invention provides for an extension of the fuel intake time in order to accumulate, prior to injection, and by a corresponding choice of the throttle means, the largest admissible amount of injection fuel at the highest admissible rpm over the en- 3 tire duration from the end of a preceding injection till the beginning of the next following work stroke. This provides an automatic safety control, for whenever the maximum rpm is exceeded, an automatic reduction of the injected amount of fuel will occur, because at increasing rpm, the intake will not suffice for completely filling the pump work space.

A particularly rapid and therefore advantageous operation of the fuel injection system according to the invention is achieved by providing for pressure-relief of the solenoid valves and by having the latter contain a ball as the movable valve member. The small masses that must thus be moved in these valves permit the valves to be shifted almost without delay, and this is in turn of advantage for obtaining a rapid and exact operation of the entire system.

In order to prolong the injection time at small load and/or at small rpms a further embodiment of the invention provides for the pressure of the fuel fed from a pressure source to the servo piston being dependent on the rpm and/or on the load of the engine.

The velocity of stroke of the pump piston and consequently the course of the injection are made variable in an advantageous manner by providing a lug or the like abutment means to project from that frontal end of the servo piston which adjoins the servo pressure space; this abutment means protrudes with a clearance into a control bore between the valve slide and the servo pressure space and leaves in the servo bore a passage for fuel flow the cross sectional area of which varies dependent on the stroke position of the servo piston.

The invention will be better understood and further objects and advantages will become apparent from the ensuing detailed specification of preferred but merely exemplary embodiments taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS.

FIG. 1 represents an axial sectional view of the pump-and-nozzle unit of a first embodiment of a fuel injection system according to the invention.

FIG. 2 represents an axial sectional view of the same pump-andmozzle unit, however, turned about its axis by an angle of 90, and taken in a sequence of planes as indicated by the dash-and-dotted line designated by IIII in FIG. 1, and, moreover, showing the servo piston and the pump piston in their respective top center positions.

FIG. 3 is a highly schematical view ofa fuel injection system according to the invention containing the pump-and-nozzle unit shown in FIGS. 1 and 2, with the valve slide thereof being in first indexing position, at the beginning of the pressure stroke.

FIG. 4 is a schematical view, similar to that of FIG. 3, of another embodiment of the fuel injection system according to the invention; and

FIGS. 5 and 6 are diagrams showing the injected fuel quantity as a function of the injection, fuel intake and control times in the case of the first embodiment, mentioned above.

DETAILED DESCRIPTION OF THE EMBODIMENTS The pump-and-nozzle assembly 10 shown in FIGS. 1 and 2 consists of three subassemblies ll, 12 and 13 which are held together by screw connections to form a single unit.

The first, upper subassembly 11 comprises a housing 14 having a first bore in the form of a stepped recess 15 in the top end of the housing and a transverse bore 16 in the portion of housing 14 which is joined to subassembly 12. In recess 15, there is lodged a first solenoid valve 17 forming a 3:2 path-valve. A valve slide 18 is slidingly guided in the transverse bore 16, one end of slide 18 being biassed by a spring 19 while its other end is exposed to a hydraulic pressure which prevails in an annular control pressure chamber 21. The admission of hydraulic fluid to the pressure chamber 21 is controlled by the solenoid valve 17.

The second subassembly is constituted by a hydraulically driven pump 12 which is controlled by the valve slide 18 via a control bore 22. The pump 12 comprises a pump housing 20, a servo piston 24, a pump piston 25, a throttle member 26 (see FIG. 2) and a liquid-feed valve 27. The frontal face 28 of the servo piston 24 forms the lower end wall of a servo pressure space 29, the upper end wall of which is formed by the lower frontal face 88 of a sleeve member 31 containing an axial control bore 22. The upper portion of sleeve member 31 is inserted in a recess 22b of enlarged diameter in the bottom part of housing 14 in which recess an axial bore 22a opens to register with control bore 22. With its reduced diameter portion sleeve member 31 protrudes into an axial recess 23 in pump housing 20.

The third subassembly which constitutes an injection nozzle 13 of known construction (see FIG. 2) is joined in coaxial alignment to the second subassembly 12 and comprises a spring housing 32, an intermediary disc member 33 and a hollow nozzle body 34. A valve needle 35 is guided in the nozzle body 34, and is biassed by a return spring 38 toward closed position. A generally sleeve-shaped tightening nut 40 encloses all elements of the injection nozzle 13 and secures them on the housing 20 of pump 12, by being fastened with internal threading 40a, in its open top end, on to an externally threaded lower end portion 20a of the pump housing 20.

The injection nozzle 13 shown in FIGS. 1 and 2 is of the inwardly opening type. Of course, a nozzle of the outwardly opening type could also be used in its place, or the valve needle 35 could be made integral with the pump piston 25 and could feed the fuel quantity to be injected directly, and without interposition of a valvetype injection nozzle, through the nozzle openings into the combustion space of the engine (not shown). Such pump-and nozzle units have been described in German Pat. No. 1,058,313.

The housing 14 of the upper subassembly 11 is provided with a fuel supply bore 41 disposed at a right angle to the longitudinal axis of the pump-and-nozzle assembly 10 (see FIG. 2); a fuel supply line 43 is connected to supply bore 41 for feeding fuel to the pumpand-nozzle unit 10 under a servo pressure p from a pressure source 91 which has been shown schematically in FIG. 3 and will be described more in detail further below. From the supply bore 41, fuel flows to an annular chamber 46 of enlarged diameter in the wall of the transverse bore 16 coaxially with the latter, and from this annular chamber 46 via a fuel supply duct 47 to the stepped recess 15 and into contact with the solenoid valve 17 therein, on the one hand, and via fuel feeder conduit 48 in housing 14, via a throttle member 26 which is screwed into the top end of a fuel-feeder conduit 48a in pump 12, and via the said conduit 48a to the feed valve 27, on the other hand. When feed valve 27 is open, as is the case during the intake stroke of the pump, fuel can flow through valve 27 and from the spring chamber 49 of the latter via a port 51 to the pump work space 52 being the lower end of axial bore 23 of pump housing 20. By way of further fuel conduits 53, 53a and 53b provided in housing 32 of needle return spring 38, the pump work space 52 and feed valve spring chamber 49 connected thereto communicate at all times with an annular pressure chamber 54 which is provided in nozzle body 34 about the valve needle 35 a short way upstream of the nozzle discharge outlet 55.

The cross sectional area of the fuel passage through the throttle member 26 from conduit 48 to conduit 48a influences the feed rate of the fuel to the feed valve 27 and further to the pump work space 52, i.e., it determines the filling time t, of the pump-and-nozzle assembly 10. Due to the fact that the filling time t; can be made considerably longer than the injection time t, (for instance, eighteen times as long as the latter) essentially due to the effect of throttle member 26, a correspondingly greater accuracy in metering the amount Q of fuel to be injected can be achieved. Even very small amounts of fuel to be injected, e.g. amounts smaller than 3 mm per stroke, can be controlled very accurately owing to the feature of prolonging the filling time i As shown in FIG. 1, a fuel return conduit 57 leads from a second annular chamber 56 provided in the wall of transverse bore 16 coaxially therewith and spaced from first annular chamber 21, to another stepped recess a in the top end of subassembly housing 14, in which recess 15a there is disposed a second solenoid valve 100; and when the latter valve is open fuel can flow from recess 15a via a connecting bore 58 to a fuel return line 59 connected to the opening of bore 58 in the outer wall of housing 14. The return line 59 leads to the pressure source 91 shown in FIG. 3 and described further below.

The second solenoid valve 100 is an electromagnetically actuated pressure-relieved 2:2-path valve comprising a ball 101 as the displaceable valve member. This second solenoid valve 100 is distinguished from the first solenoid valve 17 only by the fact that it has two instead of three fuel paths connected thereto, for which reason it comprises only one valve seat 102 to be obturated by the ball 101.

The first solenoid valve 17 which shall now be described in greater detail is also pressure relieved and actuated by an electromagnet 61. It is mounted in top recess 15 of housing 14 and is shown in a sectional, somewhat simplified view in FIG. 1 and in a lateral view in FIG. 2. This valve 17 is a 3:2-path valve and comprises a valve housing 62 and, as the displaceable valve member, a ball 63 is provided therein. In the position as shown in FIG. 1, namely its closing position, ball 63 obturates a valve seat 64 and thereby blocks fuel flow from the fuel-supply duct 47 to another control duct 65 in housing 14 leading to the control pressure chamber 21. This control duct 65 and, therefore, pressure chamber 21, are, at the same time, in communication, via an unobturated second valve seat 66 for ball 63 in valve housing 62, and further via a transverse duct 67 in the housing 14 which connects recess 15 with an annular space 68 in recess 15a about the second solenoid valve 100 and through the latter space with connecting bore 58 and fuel return line 59.

The electromagnet 61 is provided with an armature 69 which is guided in a central bore of solenoid valve housing 62 and urges the ball 63 against the valve seat 64 due to being biassed by a spring 71 when the electromagnet 61 is deenergized. In order to be able to keep the closing force of spring 71, and consequently the size of the electromagnet, within acceptable limits, the solenoid valve 17 is pressure-relieved. This is achieved by exposing a chamber 73 housing the spring 71, by way of a channel 72 in housing 14 by-passing the armature 69, to the servo pressure p which prevails in the fuel supply duct 47. The surface portions of ball 63 and of the armature 69 which are exposed to the pressure of the fuel are equal or approximately equal, whereby the forces exerted on the ball 63 in the direction of opening and closing the valve seat 64 are also equal or about equal. Therefore, only the additional force of spring 71 acting in the closing direction is needed to hold the ball 63 on valve seat 64.

The second position of the solenoid valve 17, which has not been shown and would be its open" position as far as valve seat 64 is concerned, is attained when the electromagnet 61 is energized, for instance, by means of a known contactor, or by means of an electronic control unit (only shown symbolically in FIG. 3), whereby the force of spring 71 is overcome and the armature 69 is attracted. The entering fuel stream will urge the ball 63 against the second valve seat 66, whereupon fuel can flow from the fuel supply duct 47 past the first valve seat 64 into the control pressure chamber 21 in which the fuel shifts the valve slide 18 to the right (taken in FIG. 1) while overcoming the force of spring 19, and thereby causes an annular groove 74 in the cylindrical surface of valve slide 18 to register with the annular chamber 46, and thus establish communication between this chamber 46 which is under servo pressure p, and the control bore 22. Fuel will then flow through the control bore 22 and move the servo piston 24 and the pump piston 25 while flowing into the servo pressure chamber 29; for instance, when pumping the maximal amount of fuel to be injected, O pistons 24 and 25 will be moved from their top dead center position as shown in FIG. 2 to their bottom dead center position as shown in FIG. 1, whereby fuel from the pump work space 52 will be pumped via port 51 (see FIG. 2) and via the conduits 53, 53a and 53b to the annular pressure chamber 54 and to the nozzle discharge outlet 55 of injection nozzle 13, so that a fuel injection into the combustion space of the engine can take place.

The zones of the valve housing 62 of solenoid valve 17 which are subjected to pressures of different magnitude are sealed off from one another by sealing rings 76, 76a and 7612 which are placed in the correspondingly stepped sections of stepped recess 15. The second solenoid valve 100 is lodged in a similar manner in stepped recess 15a, and is sealed therein fluid-tight by means of two sealing rings and 70a.

Fuel leaking along the valve needle 35 of injection nozzle 13 which will gather in the spring chamber 39, may flow off via a bypass conduit 77 in nozzle housing 32 and pump housing 23 and via a further bypass conduit 78, being connected to conduit 77 and extending through the top housing 14, to open out into that annular zone in the stepped recess 15 which is sealed off hermetically from the other annular zones by sealing ring 76 above and sealing ring 76a at the bottom of this zone, and from this zone, the leak fuel will flow as is shown in FIG. 1, via transverse duct 67 through the housing 14 to the annular space 68 and from there to the fuel return line 59.

Fuel leaking past pistons 24 and 25 will gather in an enlarged diameter annular chamber 79 of axial bore 23 in pump housing 20, which bore is in communication with conduits 77 and 78; in this chamber 79, the contact face between servo piston 24 and pump piston 25 comes to be located when the pistons are in top center position, as shown in FIG. 2. A check valve 81 is threaded into the part of conduit 78 extending through pump housing and prevents fuel from being siphoned back during the return stroke of the servo piston 24, from the fuel return line 59 and/or the part of conduit 78 in top housing 14, for this may impede the downward movement of the servo piston 24 during the injection stroke.

In order to be able to influence the stroke velocity of the pump piston (FIG. 1) during the pressure stroke, and thereby the course of the injection, the servo piston 24 driving the pump piston 25 is provided with an extension 82, protruding from its frontal face 28, which has the shape of a conical nose in the embodiment shown in FIGS. 1 and 2. The nose 82 plunges into the control bore 22 and leaves therein a flow passage 83 the cross sectional area of which varies along the nose 82 and is moreover dependent on the stroke position H of the servo piston 24, whereby the stroke velocity of the pump piston 25 and, together therewith, the course of the injection can be varied. The variation of the cross sectional area of flow passages 83 can also be achieved with a cylindrical extension 82 by providing the control bore with a correspondingly varying diameter (not shown in the drawings).

In the bottom dead center position (UT-position) of the pump piston 25, shown in FIG. 1, the pump working space 52 is connected via a channel 85 through piston 25 with an annular chamber 86 which is of wider diameter than the adjacent cylindrical portions 23a of axial bore 23 which closely fit piston 25. Annular chamber 86 is in communication via a transverse lateral bore 87 (see FIG. 2) with the bypass conduit 77 for leak fuel in pump housing 20. This relieves the pressure in the injection nozzle 13, decreasing the same to the pressure prevailing in the fuel return line 59, i.e. to practically one bar. If a higher pressure is to be maintained in the pump work space 52, with the pump at standstill, the annular chamber 86 can be connected with the fuel supply bore 48 instead of with the bypass conduit 77, whereby the servo pressure p from the pressure source prevails in the pump work space 52 and in the nozzle 13, when the pump is at a standstill.

In FIG. I, the servo piston 24 and the pump piston 25 are shown in their bottom dead center positions, as has been explained hereinbefore. They will remain in this position in spite of the free communication, controlled by the valve slide 18, between the control bore 22 and the return conduit 57, until, in response to a corresponding control signal, the second solenoid valve 100 opens the communication, hitherto obturated by the valve member 101, between the return conduit 57 and the fuel return line 59. When the solenoid valve 100 opens (not illustrated), the intake stroke of the pumpand-nozzle unit will begin, for the servo pressure p pre- 8 vailing in the pump work space 52 will drive the pistons 24 and 25 upwardly, with the servo pressure space 29 being pressure-relieved, until the solenoid valve 100 closes again, or until the servo piston 24 has arrived at its top dead center position as shown in FIG. 2.

In this top center position at the end of its intake stroke, ie before beginning its pressure stroke, the servo piston 24 abuts with its frontal face, 28 against the frontal end face 88 of the lower cylindrical reduced diameter portion 89 of sleeve member 31, which frontal face 88 forms the upper end wall of the servo pressure space 29 as has been mentioned before. The length of the cylindrical portion 89 determines the maximal stroke H of the servo piston 24 and of the pump piston 25 and, consequently, the maximally injectable amount of fue Qmmr- By a corresponding adjustment of the stroke H it is possible, if desired, to limit the maximum injectable fuel amount Om", t0 the admissible amount of fuel to be injected at operation under full load. Thereby, it becomes impossible to inject more than the full load fuel amount even when the control means of the injection system is faulty.

In FIG. 3 there are shown in a highly schematical representation the pump-and-nozzle unit 10 and associated known component elements pertaining to the first embodiment of the fuel injection system according to the invention. The pistons 24 and 25 are in their top dead center position as shown in FIG. 2. The symbolically represented first solenoid valve 17 is, however, shown in its open" position in which the fuel supply line 43 is connected via the control duct 65 (shown here by a broken line) with the control pressure chamber 21, in which condition the valve slide 18 has been displaced to the right, against the force of the spring 19, and its annular groove 74 thus establishes communication between the supply line 43 via supply bore 41 and annular chamber 46 with the control bore 22 and through the latter with the servo pressure space 29. In this indexing position the pressure of injection stroke is commenced and takes its course until the pump piston abuts at its lower stop 90 which is constituted by the top end face of spring housing 32, where it serves as the lower wall of the pump work space 52.

The second solenoid valve is also symbolically represented as a 2:2 path valve and is shown in an indexing position in which it interrupts communication between the fuel return conduit 57 and the fuel return line 59. The pressure source 91 is connected to the fuel supply line 43.

This fuel pressure source 91 may comprise, as indicated in the present case, a gear pump 93 which is driven by the internal combustion engine 92; its fuel supply pressure can be held by means of a pressureregulating valve 94 at a desired servo pressure p, e.g. at 50 bar.

By using an appropriate type of pressure-regulating valve 94, the servo pressure-p can also be regulated to be dependent on the rpm or on the load at which the engine operates. For instance, dependence of the servo pressure p on the load can be achieved in a known manner and by means not illustrated, by changing the spring bias depending on the position of the lever regulating the drive performance of the engine (the accelerator) or by a rotary or twist adjustment of the movable valve member of the pressure regulating valve 94, which member is provided with an oblique overflow edge.

In order to compensate fluctuations of the pressure, the pressure source 91 is equipped with a pressure reservoir 95. The gear pump 93 aspirates fuel from a fuel tank 98 via a suction line 96 and a filter 97, and fuel released from the control devices of the pump-and-nozzle unit and leak fuel therefrom are returned to tank 98 via the fuel return line 59.

When the fuel injection system is attached to a multicylinder internal combustion engine, further pumpand-nozzle units (not illustrated in FIG. 3) required per working cylinder of the engine are connected to the branch lines 43a, 43b, 430 respectively of the fuel supply line 43, and to the branch lines 59a, 59b, 590 of the fuel return line 59.

The control of solenoid valves 17 and 100 is effected by a well-known and only symbolically represented control device 99 which emits switching signals for controlling the beginning of intake and that of injection to the first solenoid valve 17, and switching signals of variable length to the second solenoid valve, whereby the filling time t; and consequently the fuel amount Q to be injected can be determined, as has been stated hereinbefore.

FIG. 4 shows a second embodiment of a fuel injection device according to the invention. As in the case of the first embodiment shown in FIG. 3, the individual elements of the system have been illustrated schematically. The entire system according to the second embodiment is distinguished from that shown in- FIG. 3 merely by a slightly different pump-and-nozzle unit'l0a in which the first solenoid valve is structurally incorporated in the unit, while, in lieu of the second solenoid valve 100 (of FIG. 3) the system comprises a second solenoid valve 100a which is so interposed in the fuel return line that it is adapted to control at least one further return line 59a. A further solenoid valve 10% of the same type as the solenoid valve 100, then controls the return flow of released and leak fuel from two other pump-and-nozzle units (not shown) through the fuel return lines 59b and 59:.

In this embodiment, each of the second-type solenoid valves 100a or 100]? controls, respectively, the filling time of one of two pump-and-nozzle units. If, for instance, in the case of the first solenoid valve 17 having the indexing position shown in FIG. 4, the second solenoid valve 100a shifts to its open position, then it will have no influence on fuel flow through the return line 59, for this line is then closed by the first solenoid valve 17, but the fuel return line 59a of another pump-andnozzle unit (not illustrated) is now in communication with fuel tank 98, and the intake stroke may take place when the first solenoid valve of this not-illustrated pump-and-nozzle unit is open.

A preferred control diagram for the first embodiment according to FIGS. 1 to 3 is shown in FIG. 5. In the lower part of the diagram the curve of H of pump piston and consequently the injection amount Q has been plotted against the intake period i the injection period 1,. and the control period t The maximally possible injection amount Omar; .e., the highest peak of curve A will be attained at the stroke H and at an engine speed of, for instance, 4500 rpm and at an intake period If of 25.2 milliseconds (ms), the corresponding injection period I, being in this case 1.5 ms. Both periods together correspond, in the case of curve A, to a cam angle of 360, i.e., to one whole revolution of the camshaft. In a four-stroke engine, one revolution of the camshaft corresponds to two revolutions of the crankshaft, i.e. to a crank angle (KW) of 720. Injection period and intake period together (1, t;) result in a cycle period T, between two peaks of curve A, of 26.7 ms, which period corresponds to a working cycle of the engine at an engine speed it equal to 4500 rpm; for, i

T 2.60/4500 2.360/6 X 4500 26.7 X 10 seconds 26.7 ms.

The equation T =1 t, is valid'only when, at 1 the fuel intake can begin at the same time that injection ends, due to a shifting of both the solenoid valves 17 and 100. However, this simultaneous shifting of both solenoid valves 17 and 100 at t takes place in the above-described control example only at a fuel output of O and at the full-load engine speed of n 4500 rpm, on which the example is based.

A smaller amount Q, of injected fuel (partial load injection amount) is achieved at the stroke H when the injection follows the course of the curve B, represented by a broken line. The corresponding intake period is designated as r and the corresponding injection period as r,.,. The representation of curve B in FIG. 5 is based on the assumption that the same speed n 4500 rpm will exist at 0,, for a lesser engine speed would also result in a correspondingly longer cycle period T (not shown). Between the end of r and beginning of I the pump piston 25 is in abutment at its lower stop 90 during a resting period t,,. The cycle period T is in this case the sum of t,. +t t The switching periods of the solenoid valve 17 are represented by the fully drawnout line C for the case of maximally possible injection amount Q and a line D shows the corresponding switching periods for controlling the partial load injection 6 amount Q, are represented by a broken line E for the solenoid valve 17, and by a broken line F for the second solenoid valve 100. At C and D,, E, and F,, respectively, the valves 17 and are in their closed positions, at C D E and F respectively, they are in their open positions. The beginning of the switch-on periods r, and 2, respectively, of the first solenoid valve 17 determines, based on the assumption of a constant beginning of the injection, the beginning of injection r, as well as the control of O as well as Q,. The switching periods 1, and t end at t At this instant, the time 1,. for injecting Om"Jr should also be terminated, although this is not an absolute condition. In the present example, t, is equal to t,,, whereby the circuitry of the system becomes relatively easy, for the solenoid valve 17 then needs to receive only a starting signal dependent on the cam angle.

The time interval between the two switching on periods I, and r,,, during which the solenoid valve 17 is deenergized and is in its closed position C, or E,, has been designatedas the of period t,,, or r,,,, respectively. The point on the time axis at which injection ends has been designated as t or t;,, and only depends essentially on the accumulated injection amount Q or Q,, for the other magnitudes influencing this point, such as the servo pressure p and the characteristics of the injection nozzles 13, are constants. In fact, if this is desired, the fuel servo pressure p may also be varied, for instance in dependence on the rpm of the engine, in order to vary the duration of the injection within certain given limits.

Ill

The switch-on period 1, (Line D) of the second solenoid valve 100 begins at I, for control of the intake period of the injection amount Q,,,,,,, and terminates shortly after I,. but could also coincide with the latter. The corresponding switch-off period of the solenoid valve 100 has been designated by 2.

In order to control Q,, t,,, begins simultaneously with the intake period t,, at t, and terminates at t,, or, as has been shown in the diagram, shortly after r,. The corresponding switch-off period is 13,

The switching periods of the two solenoid valves 17 and 1100 may also be controlled completely independently of one another, as illustrated in FIG. 6. The switching periods, curves and lines which correspond to those shown in FIG. 5 bear the same designations.

Between the intake period t,, or t,,, respectively, and the injection period t,. or t, a dwelling period t, or t,., has veen provided for, so that the period of a cycle is composed of the injection period, the rest period, the intake period and the dwelling period. The intake period 1,, or I begins always at t, and ends depending on the amount of injection fuel, O or 0,, to be accumulated, either at 1 or at 1 on the time axis. In order to prevent the dwelling period r, from becoming too large at small amounts of fuel to be injected, t, may also be maintained constant, and the instant I, for the beginning of the intake period I, may be varied (see for instance, point t,, on the time axis). The switching periods for the first solenoid valve 17 are constant, and its switch-on period t, begins always as t, and terminates at t,, while its off period 1,, extends from t, to r, (Line C). Control of the injection amount Q is taken over solely by the solenoid valve 100, the on periods of which, t or I determine the intake take periods I, or r,,, respectively, for the injection amounts Omar or 0,. Line E, shown in FIG. 5, which represents the switching period of the solenoid valve 17 for controlling the injection amount 0, has been omitted in FIG. 6, as it is identical with line C.

The control operation of the second embodiment illustrated in FIG. 4, could be represented by a diagram derived from that of FIG. 6, wherein only the intake period t, would have to be divided in such a manner that during this same period there would take place the intakes, independently of one another, of two pump-andnozzle units. By a corresponding prolongation of t, for each of the two solenoid valves I7 in these units, the fuel return line 59 (see FIG. 4) would remain closed for such a time as would be required by the solenoid valve Ia for controlling the intake period by establishing communication between the conduit 59a and the fuel tank 98.

DESCRIPTION OF THE OPERATION DURING ONE WORK CYCLE In the following there will be described the operation of the first embodiment of a fuel injection system according to the invention during one full work cycle, with reference to FIGS. I, 2, 3 and 5. Prior to the beginning of the injection of the full-load fuel quantity O (see FIGS. 2 and 3 and the curves A, C and D in FIG. the servo piston 24 abuts at H,,,,,,, as a result of the preceding intake stroke, with its frontal face 28 against its upper stop, namely the lower end face 88 of sleeve member 31 (top dead center or OT-position). At t,, the solenoid valve 17 switches from the closed position C, to the open position C Thereby, ball 63 (FIG. 1) is lifted from its valve seat 64 to rest on the valve seat 66, and fuel being fed under the servo pressure p from the pressure source 91 flows into the servo pressure space 29 (FIG. 3). The fuel now acts upon the aforesaid frontal face 28 of servo piston 24 and drives the latter, and together therewith the pump piston 25, downwardly until the pump piston 25 arrives at the instant in its bottom dead center position (UT- position) (see FIG. 1). During its downward movement, the pump piston 25 carries out its maximum stroke H (FIG. 2) and delivers the fuel present in the pump work space 52 via port 51 and fuel conduits 53, 53a and 53b to the nozzle discharge outlet 55 of the injection nozzle 13. In the pump work space 52, there is thus generated an injection pressure p of, e.g., 300 bar which is larger, depending on the transmission ratio of servo piston 24 to pump piston 25, than the servo pressure which may be, e.g., 50 bar. The return spring 38 of injection nozzle 13 is biassed, in the instant example, for a nozzle opening pressure of bar, and the fuel being under the injection pressure p, acts on the valve needle 35 and raises the same, whereby the injection amount O of fuel delivered by the pump piston 25 will be injected in a known manner into the cylinder of the engine.

At the point t on the time axis (FIG. 5), at which injection ends, the solenoid valve 17 switches, after the on period 1,, from its open position C back to its closed position C, (FIG. 1). The ball 63 now cuts off fuel flow to the control pressure chamber 21 and relieves the latter of pressure by admitting fuel therefrom via the control duct 64 and past the now unobturated valve seat 66 to the fuel return line 59 and the tank 98. The spring 19 now urges the valve slide 18 back into its initial position shown in FIG. 1, in which position the annular groove 74 in slide 18 establishes communication between the servo pressure space 29 and the fuel return conduit 57 while the latter is connected, due to the simultaneous switching of the second solenoid valve I00 from itsclosed position D, to its open position D to the fuel return line 59 and the tank 98 of the system. This causes the fuel pressure in the servo pressure space 29 and in the pump work space 52 to drop abruptly, the fuel feed valve 27 will open and the fuel under servo pressure 1 will drive the pump piston 25 and the servo piston 24 away from its UT-position during an intake period t, which is prolonged due to the effect of throttle member 26. This fuel intake operation takes place during the intake period I between t and r,, until, at t,, the solenoid valve 17 switches again to its indexing position C described hereinbefore, and the next following working cycle begins. At t,, or as shown in FIG. 5, shortly after t,, the second solenoid valve I00 switches back from D, to D,. In this case the intake period t, is equal to the of period of the solenoid valve 17.

The cross sectional area of fuel flow through the throttle member 26 which is inserted in the fuel supply conduit 48, influences the flow rate of the fuel to the pump work space 52, i.e., it determines the intake period t, of the pump-and-nozzle unit 10. Due to the fact that the intake time t, is considerably prolonged, owing to the flow of fuel through the throttle member 26, over the injection period n, (e.g., 18 times), a correspondingly greater accuracy of metering the injection fuel quantity can be achieved. Even very small injection fuel amounts (less than 3 mm per stroke) can be controlled very accurately due to this prolonged intake period I,.

An automatic safety regulation is obtained by extending the intake period t; by a corresponding layout of the throttle bore in throttle member 26, and at the maximally admissible rpm (n over the entire period between the end point of injection t, of a given work cycle T and the beginning of injection, t,, of the next following work cycle T, as is indicated by curve A in the example described above. Exceeding the maximal rpm will thus lead to an automatic reduction of the amount of fuel to be injected because, at increasing rpm, the intake period which is independent of the rpm, would not be sufficient for completely filling the pump work space 52.

During the delivery of the partial-load injection amount 0,, as illustrated by curves B, E and F in FIG. 5, and at a stroke H,, only an injection amount Q, corresponding to this stroke has been accumulated, for the next following injection, during the intake period t,, lasting from t, to 1,. At the instant t,, as the solenoid valve 17 switches from E, to E there begins an intake period which ends at 1 At t the solenoid valve 17 switches back from E to E, which, however, does not influence the course of the injection as the return line 59 is still closed by the second solenoid valve 100. Up to the point t, on the time axis, at which the second solenoid valve 100 is switched from F, to F the pump piston 25 will remain during its rest period t,, in the UT-position shown in FIG. 1. As solenoid valve 100 is switched from its closed position F, to its open position F at the point t,, the intake stroke begins which proceeds during the intake period t,, to the point t, on the time axis. The next injection will begin at t, and the entire above-described work cycle will be repeated.

A pressure regulating valve 94 for regulating the servo pressure p dependent on the load or rpm has been described in my earlier patent application Ser. No. 257,386, filed on May 26, 1972, and also assigned to the same assignee.

What is claimed is:

1. In a fuel injection system for an internal combustion engine having a pump-and-nozzle assembly per cylinder which assembly comprises a pump piston and a pump work space therefor; a servo piston having a larger diameter than said pump piston and driving the latter; a pressure source to which said assembly is connected; a servo pressure space, limited on one side thereof by a frontal face of said servo piston; a fuel feed valve; said pressure source being adapted for delivering fuel to said pump work space via said fuel feed valve as well as to said servo pressure space; a valve slide adapted for being driven by a portion of the fuel delivered by said pressure source; and a fuel return line and a control device for controlling said valve slide synchronously with the work cycle of the engine, wherein said valve slide controls in a first indexing position the flow of fuel to said servo pressure space, and in a second indexing position the flow of fuel from said servo pressure space to said fuel return line, thereby rendering possible the return stroke of said servo piston and simultaneously the intake stroke of said pump piston,

the improvement of each pump-and-nozzle assembly in said system comprising a. a 3:2-path solenoid valve being disposed near said valve slide and being adapted, when energized, for

establishing communication between said pressure source and said valve slide, whereby the latter is movable into said first indexing position initiating the injection of fuel;

b. a pre-set throttle member being interposed between said pressure source and said fuel feed valve and being adapted for influencing the velocity of the intake stroke of said pump piston; and

c. a 2:2-path solenoid valve interposed in said fuel return line and comprising adjusting means for varying the opening periods thereof, thereby determining, in a second indexing position of said valve slide, the duration and length of the intake stroke of said pump piston and together therewith the amount of fuel delivered in the interval between two fuel injections.

2. The improvement as described in claim 1, wherein said return fuel line in which said 2:2-path solenoid valve is interposed comprises at least one branch line connected to a further pump-and-nozzle' assembly in said system, whereby said 2:2-path solenoid valve controls the duration of the intake stroke of the pump piston of each such further pump-and-nozzle assembly.

3. The improvement as described in claim 1, wherein said system comprises stroke limiting means associated with said pump piston for setting a maximally admissible stroke of said pump piston, thereby controlling the maximal amount of fuel to be injected per work cycle.

4. The improvement as described in claim 3, wherein said throttle member is so dimensioned relative to said maximal pump piston stroke that the intake period of said pump piston for taking in the maximally admissible amount of fuel to be injected during a work cycle at the highest permissible rpm of the engine is extensible to the entire period of from the time of ending an injection till the time of beginning the next following work cycle.

5. The improvement as described in claim 1, wherein each of said solenoid valves is pressure-relieved and comprises'a ball as the movable valve member.

6. The improvement as described in claim 1, wherein said assembly further comprises pressure regulating means for adjusting the servo pressure of the fuel supplied from said pressure source to said servo piston dependent on the rpm of the engine.

7. The improvement as described in claim 1, wherein said assembly further comprises pressure regulating means for adjusting the servo pressure of the fuel supplied from said pressure source to said servo piston dependent on the load under which said engine operates.

8. The improvement as described in claim 1, wherein said servo piston bears a projection on said frontal face thereof limiting said servo pressure space; and wherein said assembly comprises a control bore interposed between said valve slide and said servo pressure space, said projection protruding into said control bore and leaving within the latter, when at rest relative to said bore, a fuel flow passage of a cross-sectional area which varies in axial direction of said bore, whereby the crosssectional area of said passage is further varied when said projection is displaced relative to said control passage during a stroke of said servo piston. 

1. In a fuel injection system for an internal combustion engine having a pump-and-nozzle assembly per cylinder which assembly comprises a pump piston and a pump work space therefor; a servo piston having a larger diameter than said pump piston and driving the latter; a pressure source to which said assembly is connected; a servo pressure space, limited on one side thereof by a frontal face of said servo piston; a fuel feed valve; said pressure source being adapted for delivering fuel to said pump work space via said fuel feed valve as well as to said servo pressure space; a valve slide adapted for being driven by a portion of the fUel delivered by said pressure source; and a fuel return line and a control device for controlling said valve slide synchronously with the work cycle of the engine, wherein said valve slide controls in a first indexing position the flow of fuel to said servo pressure space, and in a second indexing position the flow of fuel from said servo pressure space to said fuel return line, thereby rendering possible the return stroke of said servo piston and simultaneously the intake stroke of said pump piston, the improvement of each pump-and-nozzle assembly in said system comprising a. a 3:2-path solenoid valve being disposed near said valve slide and being adapted, when energized, for establishing communication between said pressure source and said valve slide, whereby the latter is movable into said first indexing position initiating the injection of fuel; b. a pre-set throttle member being interposed between said pressure source and said fuel feed valve and being adapted for influencing the velocity of the intake stroke of said pump piston; and c. a 2:2-path solenoid valve interposed in said fuel return line and comprising adjusting means for varying the opening periods thereof, thereby determining, in a second indexing position of said valve slide, the duration and length of the intake stroke of said pump piston and together therewith the amount of fuel delivered in the interval between two fuel injections.
 2. The improvement as described in claim 1, wherein said return fuel line in which said 2:2-path solenoid valve is interposed comprises at least one branch line connected to a further pump-and-nozzle assembly in said system, whereby said 2:2-path solenoid valve controls the duration of the intake stroke of the pump piston of each such further pump-and-nozzle assembly.
 3. The improvement as described in claim 1, wherein said system comprises stroke limiting means associated with said pump piston for setting a maximally admissible stroke of said pump piston, thereby controlling the maximal amount of fuel to be injected per work cycle.
 4. The improvement as described in claim 3, wherein said throttle member is so dimensioned relative to said maximal pump piston stroke that the intake period of said pump piston for taking in the maximally admissible amount of fuel to be injected during a work cycle at the highest permissible rpm of the engine is extensible to the entire period of from the time of ending an injection till the time of beginning the next following work cycle.
 5. The improvement as described in claim 1, wherein each of said solenoid valves is pressure-relieved and comprises a ball as the movable valve member.
 6. The improvement as described in claim 1, wherein said assembly further comprises pressure regulating means for adjusting the servo pressure of the fuel supplied from said pressure source to said servo piston dependent on the rpm of the engine.
 7. The improvement as described in claim 1, wherein said assembly further comprises pressure regulating means for adjusting the servo pressure of the fuel supplied from said pressure source to said servo piston dependent on the load under which said engine operates.
 8. The improvement as described in claim 1, wherein said servo piston bears a projection on said frontal face thereof limiting said servo pressure space; and wherein said assembly comprises a control bore interposed between said valve slide and said servo pressure space, said projection protruding into said control bore and leaving within the latter, when at rest relative to said bore, a fuel flow passage of a cross-sectional area which varies in axial direction of said bore, whereby the cross-sectional area of said passage is further varied when said projection is displaced relative to said control passage during a stroke of said servo piston. 